# How to apply negtive pressure to outlet

 Register Blogs Members List Search Today's Posts Mark Forums Read May 31, 2006, 22:44 How to apply negtive pressure to outlet #1 bioman66 Guest   Posts: n/a Hi. I want to use CFX to solve this kind of problem : Chamber (A) is link with chamber (B) by a long silicin tubing. Chamber(A) contains water inside with a top little hole to the atmosphere and Chamber(B) is empty. A negtive pressure is applied at a top little hole of chamber(B). I want to simulate the flow pattern when water is sucked from chamber(A) to chamber(B). I set the reference pressure to 1 atm and opening pressure to 0 pa at the hole of chamber(A) and opening pressure to -1.05 Mpa to the hole of chamber (B). After calculation, the results is not reasonable. Could anyone can tell me how to set the boundary conditions on these chambers?  June 1, 2006, 04:17 Re: How to apply negtive pressure to outlet #2 Joe Guest   Posts: n/a How are you modelling the problem? Post your command file + pic of your geometry ... How on earth is creating a -1 MPa vacuum suction physically viable in air?  June 1, 2006, 10:44 Re: How to apply negtive pressure to outlet #3 garywang Guest   Posts: n/a Joe : The simple picture is shown as following Open |----| |----| |----| |---| <----- suction here |___________| | | | | | | | A | | B | | | | | ----| |----- -- | |----- | | | | | | | | | |____________| | |________________| Because I set the reference pressure to 1 atm, I think the relative pressure at opening of A should be zero, and suction pressure at B should be negtive to cause outward direction and water can move from A to B. I hope you can tell me more , please. Is it correct? Or should I use absolute pressure ?  June 1, 2006, 10:45 Re: How to apply negtive pressure to outlet #4 garywang Guest   Posts: n/a sorry ! this pic can not be shown corretly.  June 1, 2006, 10:57 Re: How to apply negtive pressure to outlet #5 Joe Guest   Posts: n/a Post your command file + a proper pic of your geometry. We need decent input information to offer advice, we arnt telepathic. www.imagedump.com could be usefull for hosting your images ...  June 3, 2006, 02:40 Re: How to apply negtive pressure to outlet #6 garywang Guest   Posts: n/a Dear Joe I have post my pic on the www.imagedump.com. The file name is container, user's name is bioman. The command file is shown as following: ------------------------------------------------------------ Installed patches: * Service Pack 1 Setting up CFX-5 Solver run ... +--------------------------------------------------------------------+ | | | CFX Command Language for Run | | | +--------------------------------------------------------------------+ LIBRARY: CEL: EXPRESSIONS: DenWater = 998 [kg m^-3] levelini = 0.08 [m] VFWater = step((levelini-y)/1[m]) PressIni = DenWater*g *VFWater*(levelini-y) VFAir = 1-VFWater END END MATERIAL: Air at 25 C Material Description = Air at 25 C and 1 atm (dry) Material Group = Air Data, Constant Property Gases Option = Pure Substance Thermodynamic State = Gas PROPERTIES: Option = General Material Thermal Expansivity = 0.003356 [K^-1] ABSORPTION COEFFICIENT: Absorption Coefficient = 0.01 [m^-1] Option = Value END DYNAMIC VISCOSITY: Dynamic Viscosity = 1.831E-05 [kg m^-1 s^-1] Option = Value END EQUATION OF STATE: Density = 1.185 [kg m^-3] Molar Mass = 28.96 [kg kmol^-1] Option = Value END REFRACTIVE INDEX: Option = Value Refractive Index = 1.0 [m m^-1] END SCATTERING COEFFICIENT: Option = Value Scattering Coefficient = 0.0 [m^-1] END SPECIFIC HEAT CAPACITY: Option = Value Reference Pressure = 1 [atm] Reference Specific Enthalpy = 0. [J/kg] Reference Specific Entropy = 0. [J/kg/K] Reference Temperature = 25 [C] Specific Heat Capacity = 1.0044E+03 [J kg^-1 K^-1] Specific Heat Type = Constant Pressure END THERMAL CONDUCTIVITY: Option = Value Thermal Conductivity = 2.61E-02 [W m^-1 K^-1] END END END MATERIAL: Water Material Description = Water (liquid) Material Group = Water Data, Constant Property Liquids Option = Pure Substance Thermodynamic State = Liquid PROPERTIES: Option = General Material Thermal Expansivity = 2.57E-04 [K^-1] ABSORPTION COEFFICIENT: Absorption Coefficient = 1.0 [m^-1] Option = Value END DYNAMIC VISCOSITY: Dynamic Viscosity = 8.899E-4 [kg m^-1 s^-1] Option = Value END EQUATION OF STATE: Density = 997.0 [kg m^-3] Molar Mass = 18.02 [kg kmol^-1] Option = Value END REFRACTIVE INDEX: Option = Value Refractive Index = 1.0 [m m^-1] END SCATTERING COEFFICIENT: Option = Value Scattering Coefficient = 0.0 [m^-1] END SPECIFIC HEAT CAPACITY: Option = Value Reference Pressure = 1 [atm] Reference Specific Enthalpy = 0.0 [J/kg] Reference Specific Entropy = 0.0 [J/kg/K] Reference Temperature = 25 [C] Specific Heat Capacity = 4181.7 [J kg^-1 K^-1] Specific Heat Type = Constant Pressure END THERMAL CONDUCTIVITY: Option = Value Thermal Conductivity = 0.6069 [W m^-1 K^-1] END END END END EXECUTION CONTROL: PARALLEL HOST LIBRARY: HOST DEFINITION: garywang Installation Root = C:\Program Files\Ansys Inc\CFX\CFX-%v Host Architecture String = intel_p4.sse2_winnt5.1 END END PARTITIONER STEP CONTROL: Multidomain Option = Independent Partitioning Runtime Priority = Standard MEMORY CONTROL: Memory Allocation Factor = 1.0 END PARTITIONING TYPE: MeTiS Type = k-way Option = MeTiS Partition Size Rule = Automatic END END RUN DEFINITION: Definition File = D:/icem_dir/tidecellbag/test3.def Interpolate Initial Values = Off Run Mode = Full END SOLVER STEP CONTROL: Runtime Priority = Standard EXECUTABLE SELECTION: Double Precision = Off END MEMORY CONTROL: Memory Allocation Factor = 1.0 END PARALLEL ENVIRONMENT: Number of Processes = 1 Start Method = Serial END END END FLOW: DOMAIN: fluid Coord Frame = Coord 0 Domain Type = Fluid Fluids List = Air at 25 C,Water Location = Assembly BOUNDARY: fluid Default Boundary Type = WALL Location = WALL1 1,WALL1 10,WALL1 11,WALL1 12,WALL1 13,WALL1 14,WALL1 \ 15,WALL1 16,WALL1 17,WALL1 18,WALL1 19,WALL1 2,WALL1 20,WALL1 \ 21,WALL1 22,WALL1 23,WALL1 24,WALL1 25,WALL1 26,WALL1 3,WALL1 \ 4,WALL1 5,WALL1 6,WALL1 7,WALL1 8,WALL1 9,WALL2 1,WALL2 10,WALL2 \ 11,WALL2 12,WALL2 13,WALL2 14,WALL2 15,WALL2 2,WALL2 3,WALL2 4,WALL2 \ 5,WALL2 6,WALL2 7,WALL2 8,WALL2 9 BOUNDARY CONDITIONS: WALL INFLUENCE ON FLOW: Option = No Slip END END END BOUNDARY: inlet Boundary Type = OPENING Location = IN BOUNDARY CONDITIONS: FLOW DIRECTION: Option = Normal to Boundary Condition END FLOW REGIME: Option = Subsonic END MASS AND MOMENTUM: Option = Opening Pressure and Direction Relative Pressure = 0 [atm] END END FLUID: Air at 25 C BOUNDARY CONDITIONS: VOLUME FRACTION: Option = Value Volume Fraction = 1 END END END FLUID: Water BOUNDARY CONDITIONS: VOLUME FRACTION: Option = Value Volume Fraction = 0 END END END END BOUNDARY: outlet Boundary Type = OPENING Location = OUT BOUNDARY CONDITIONS: FLOW DIRECTION: Option = Normal to Boundary Condition END FLOW REGIME: Option = Subsonic END MASS AND MOMENTUM: Option = Opening Pressure and Direction Relative Pressure = -1000 [Pa] END END FLUID: Air at 25 C BOUNDARY CONDITIONS: VOLUME FRACTION: Option = Value Volume Fraction = 1 END END END FLUID: Water BOUNDARY CONDITIONS: VOLUME FRACTION: Option = Value Volume Fraction = 0 END END END END DOMAIN MODELS: BUOYANCY MODEL: Buoyancy Reference Density = 1.185 [kg m^-3] Gravity X Component = 0 [m s^-2] Gravity Y Component = -9.8 [m s^-2] Gravity Z Component = 0 [m s^-2] Option = Buoyant BUOYANCY REFERENCE LOCATION: Option = Automatic END END DOMAIN MOTION: Option = Stationary END MESH DEFORMATION: Option = None END REFERENCE PRESSURE: Reference Pressure = 1 [atm] END END FLUID: Air at 25 C FLUID MODELS: FLUID BUOYANCY MODEL: Option = Density Difference END MORPHOLOGY: Option = Continuous Fluid END END END FLUID: Water FLUID MODELS: FLUID BUOYANCY MODEL: Option = Density Difference END MORPHOLOGY: Option = Continuous Fluid END END END FLUID MODELS: COMBUSTION MODEL: Option = None END HEAT TRANSFER MODEL: Homogeneous Model = Off Option = None END THERMAL RADIATION MODEL: Option = None END TURBULENCE MODEL: Option = Laminar END END FLUID PAIR: Air at 25 C | Water INTERPHASE TRANSFER MODEL: Interface Length Scale = 1. [mm] Option = Mixture Model END MASS TRANSFER: Option = None END SURFACE TENSION MODEL: Option = None END END INITIALISATION: Option = Automatic FLUID: Air at 25 C INITIAL CONDITIONS: VOLUME FRACTION: Option = Automatic with Value Volume Fraction = VFAir END END END FLUID: Water INITIAL CONDITIONS: VOLUME FRACTION: Option = Automatic with Value Volume Fraction = VFWater END END END INITIAL CONDITIONS: Velocity Type = Cartesian CARTESIAN VELOCITY COMPONENTS: Option = Automatic with Value U = 0 [m s^-1] V = 0 [m s^-1] W = 0 [m s^-1] END STATIC PRESSURE: Option = Automatic with Value Relative Pressure = PressIni END END END MULTIPHASE MODELS: Homogeneous Model = On FREE SURFACE MODEL: Option = Standard END END END OUTPUT CONTROL: RESULTS: File Compression Level = Default Option = Standard END TRANSIENT RESULTS: Transient Results 1 File Compression Level = Default Include Mesh = No Option = Selected Variables Output Variables List = Absolute Pressure,Pressure,Total \ Pressure,Water.Velocity,Water.Volume Fraction Time Interval = 0.02 [s] END END SIMULATION TYPE: Option = Transient INITIAL TIME: Option = Automatic with Value Time = 0 [s] END TIME DURATION: Option = Total Time Total Time = 10 [s] END TIME STEPS: Option = Timesteps Timesteps = 0.02 [s] END END SOLUTION UNITS: Angle Units = [rad] Length Units = [m] Mass Units = [kg] Solid Angle Units = [sr] Temperature Units = [K] Time Units = [s] END SOLVER CONTROL: ADVECTION SCHEME: Option = High Resolution END CONVERGENCE CONTROL: Maximum Number of Coefficient Loops = 2 Timescale Control = Coefficient Loops END CONVERGENCE CRITERIA: Residual Target = 1.E-4 Residual Type = RMS END TRANSIENT SCHEME: Option = Second Order Backward Euler END END END COMMAND FILE: Version = 10.0 Results Version = 10.0 END +--------------------------------------------------------------------+ | | | Solver | | | +--------------------------------------------------------------------+ +--------------------------------------------------------------------+ | | | ANSYS CFX Solver 10.0 | | | | Version 2005.10.25-23.10 Tue Oct 25 23:48:51 GMTDT 2005 | | | | Executable Attributes | | | | single-32bit-optimised-supfort-noprof-nospag-lcomp | | | | Copyright 1996-2005 ANSYS Europe Ltd. | +--------------------------------------------------------------------+ +--------------------------------------------------------------------+ | Job Information | +--------------------------------------------------------------------+ Run mode: serial run Host computer: GARYWANG Job started: Sat Jun 3 13:25:36 2006 +--------------------------------------------------------------------+ | Memory Allocated for Run (Actual usage may be less) | +--------------------------------------------------------------------+ Data Type Kwords Words/Node Words/Elem Kbytes Bytes/Node Real 9818.0 455.89 536.33 38351.7 1823.56 Integer 1907.2 88.56 104.18 7450.0 354.24 Character 2433.1 112.98 132.91 2376.0 112.98 Logical 40.0 1.86 2.19 156.2 7.43 Double 227.7 10.57 12.44 1778.7 84.57 +--------------------------------------------------------------------+ | Total Number of Nodes, Elements, and Faces | +--------------------------------------------------------------------+ Domain Name : fluid Total Number of Nodes = 21536 Total Number of Elements = 18306 Total Number of Hexahedrons = 18306 Total Number of Faces = 6158 +--------------------------------------------------------------------+ | Buoyancy Reference Information | +--------------------------------------------------------------------+ Domain Group: fluid Buoyancy has been activated. The absolute pressure will include hydrostatic pressure contribution, using the following reference coordinates: ( 1.90000E-01, 4.10577E-01,-5.44734E-02). +--------------------------------------------------------------------+ | Average Scale Information | +--------------------------------------------------------------------+ Domain Name : fluid Global Length = 1.1916E-01 Minimum Extent = 1.0000E-01 Maximum Extent = 4.1058E-01 Air at 25 C.Density = 1.1850E+00 Air at 25 C.Dynamic Viscosity = 1.8310E-05 Air at 25 C.Velocity = 0.0000E+00 Air at 25 C.Mass (Conservative) = 9.8683E-04 Air at 25 C.Mass (Normalised) = 9.8683E-04 Air at 25 C.Volume = 8.3277E-04 Air at 25 C.Volume Fraction = 4.9222E-01 Water.Density = 9.9700E+02 Water.Dynamic Viscosity = 8.8990E-04 Water.Velocity = 0.0000E+00 Water.Mass (Conservative) = 8.5653E-01 Water.Mass (Normalised) = 8.5653E-01 Water.Volume = 8.5911E-04 Water.Volume Fraction = 5.0778E-01 Water.Wave Speed = 1.0806E+00 Water.Froude Number = 0.0000E+00 +--------------------------------------------------------------------+ | Writing Selected transient file Transient Results 1: 0.trn | +--------------------------------------------------------------------+ +--------------------------------------------------------------------+ | Checking for Isolated Fluid Regions | +--------------------------------------------------------------------+ No isolated fluid regions were found. +--------------------------------------------------------------------+ | The Equations Solved in This Calculation | +--------------------------------------------------------------------+ Subsystem : Momentum and Mass U-Mom-Bulk V-Mom-Bulk W-Mom-Bulk P-Vol Subsystem : Volume Fractions Mass-Water CFD Solver started: Sat Jun 3 13:25:41 2006 Thread Tools Search this Thread Show Printable Version Email this Page Search this Thread: Advanced Search Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are Off Pingbacks are On Refbacks are On Forum Rules Similar Threads Thread Thread Starter Forum Replies Last Post Eric CFX 7 May 23, 2014 09:13 a.lynchy FLUENT 3 February 13, 2012 05:03 engahmed FLUENT 0 June 13, 2010 16:33 emueller CFX 0 May 5, 2009 12:08 raivish Siemens 2 January 11, 2006 04:00

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